July 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
This work was done under a cooperative agreement between the Bureau of Mines, United States Department of the Interior, and the University of Wyoming. The authors wish to thank J. C. Neel, I. W. Kinney, and’R. T. Moore who performed various analyses reported in this paper. LITERATURE CITED
(1) Aluise, V. A., Hall, R. T., Staats, F. C., and Becker, W. W., A n a l . Chem., 19, 347 (1947). ( 2 ) Am. SOC.Testing Materials, A.S.T.M. Designation D 381-49. (3) Ibid., D 873-49. (4) Ball, J. S.,Dinneen, G. U., Smith, J. R., Bailey, C. W., and Van Meter, R., IND.ENC. CHEM.,41, 581 (1949). (5) Brooks, B. T., Ibid., 18, 1198 (1926). (6) Caesar. H. A,. Ibid.. 23. 1132 (1931). (7) Dryer,’C. G.,’Lowry, C’. D., JG., Morrell, J. C., and Egloff, G., Ibid., 26, 885 (1934).
1607
(8) Flood, D. T., Hladky, J. W., and Edgar, G., I b d . , 25, 1234 (1933). (9) Mapstone, G. E., Petroleum Refiner, 28, 111 (October 1949). (10) Martin, S. M., Gruae, W. A., and L o w , A., IND.ENG.CHEM., 25, 381 (1933). (11) Moirell, J. C., Dryer, C. G., Lowry, C. D., Jr., and Egloff, G., Ibid., 26, 497 (1934); 28, 465 (1936). (12) Secretary of the Interior, U. S. Bur. Mines, Rept. Invest. 4457, 49-50 (1949). (13) Story, L. G., Provine, R. W., and Bennett, H. T., IND. ENG. CHEW,21, 1079 (1929). (14) Walters, E. L., Yabroff, D. L., and Miner, H. B., Ibid., 40, 423 (1948). (15) Yule, J. A. C., and Wilson, C. P., Jr., Ibid., 23, 1254 (1931). RECBIVEDJanuary 3, 1951. Presented before the Division of Petroleum Chemistry at the 118th Meeting of the AMERICAN CHEMICAL SOCIETr, Chicago, Ill.
Equilibrium Flash Vaporization o f Petroleum Crude Oils or Fractions Method and Apparatus f o r Determination DONALD F. OTHMER, E. H. TEN EYCKl, AND STATLEY TOLIN2 Polytechnic Institute of Brooklyn, Brooklyn, N . Y .
T h e process engineer frequently requires vapor-liquid equilibrium data for the design of equipment to separate multicomponent hydrocarbon mixtures. Data for the more complex systems are usually expressed as a family of isobaric curves on a plot of per cent vaporized versus temperature. A new method and a new type of apparatus for the study of these vapor-liquid phase relations are presented bhich are believed to be superior to the regular equipment currently in use. This has been accomplished by the design and use of a modified recirculating equilibrium still of the type used by numerous investigators with binary and ternary systems. The unit has been thoroughly evaluated at atmospheric and subatmospheric pressures for equilibrium conditions, entrainment, and pressure drop. Tests on a variety of petroleum stocks have shown this unit to be highly satisfactory for the determination of equilibrium vaporization curves, throughout practically the entire range of ratios of per cent volatilized.
I
N DESIGN calculations for equipment for the separation of multicomponent hydrocarbon mixtures it is frequently necessary to predict vapor-liquid equilibrium relations for mixtures of various unknown compositions at different amounts vaporized. The most common method of expressing these equilibrium data is by means of a so-called L‘equilibriumflash vaporization curve.” For a given mixture and a t a fixed pressure, the temperatures of the vapor-liquid phases in equilibrium with each other are plotted against the volume per cent of the material vaporized. These 1 2
Present address, E. I. du Pont de Nemours & Co., Ino., Belle, W. Va. Present address, General Foods Corp., Hoboken, N. J.
data are then used in the design of such units as d%tilTation columns, vaporizers, and condensers. Phase equilibrium data of this type are difficult to determine by the regular methods; and the common practice is to predict equilibrium flash vaporization curves from the results of standard American Society for Testing Materials or true boiling point distillations by empirical methods. This paper presents a method and equipment which make the determination of equilibrium flash vaporization curves a simple direct’ procedure ueing bench apparatus. These equilibrium data are at present determined in continuous vaporizers (3, 4, 8, 9),which, essentially, consist of a reproduction on a small scale of a continuous distillation plant, and t h u s require a complete set of controls, sufficient feed stock, and time t o come t o steady operating conditions. There are a feed supply tank with suitable back-pressure t o cause flow through the apparatus, a heating coil to heat the fluid t o the desired temperature, a disengaging section where the vapor is separated from the liquid, and a device for measuring the quantity of the liquid and condensed vapor streams. In addition, means are supplied for measuring the temperature and pressure in the disengaging section. A unit of this type has several disadvantages. The original cost of the equipment and controls is high. It requires a large operating space. The unit is continuous in operation and requires a large tes% sample and carefully controlled feed and other operating conditions. The exact point of equilibrium is often in doubt, owing to t h e changing pressure along the transfer line between the heater an& separator. The unit requires considerable time of highly skilled technicians for satisfactory operation.
.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Data on equilibrium vaporization curves have been presented by Edmister et al. ( 4 ) , Edmister and Pollock (S),Leslie and Good (9), Piroomov and Beiswenger ( 1 7 ) , Peters (If?),Fancher (6),and Bahlke and Kay (1). Most of these curves have been obtained at atmospheric pressure or higher; however, many petroleum fractions are treated under subatmospheric conditions to prevent thermal decomposition, and design data in this region are lacking. Furthermore, because of cost and complexity of equipment, very few petroleum laboratories are equipped with these continuous units to evaluate crudes or fractions from processing equipment
THEWPMETER WELL IOmmlD
JACKE NOZZLI
JACKET NOZZLE
Figure 1. Equilibrium Still
EQU1LIBRIUII.I APPARATUS
A unit has been designed and tested for obtaining equilibrium flash vaporization data without the disadvantages listed above. A principle long employed (11-16) in numerous laboratories for vapor-liquid studies was adapted to this type of determination. This is the recirculating equilibrium still, which consists of a unit where vapor in equilibrium with a boiling liquid is passed into a condenser, and the condensate is collected in a reservoir and then recirculated back into the boiling liquid. TT7hen the entire still has reached a steady state, the equilibrium vapor coming from the boiling liquid is of the same composition as the recirculating condensed vapor. At this point the temperatures of the saturated vapor and of the liquid in the boiler remain constant. Samples of vapor condensate and boiling liquid are then taken simultaneously. In the redesign of the apparatus for the determination of equilibrium flash vaporization curves, several modifications of this type of still mere necessary. [A preferred model (11) is available from the Emil Greiner Co., 22 North Moore St., New
Vol. 43, No. 7
York, N. Y. This company supplied the present still and is able to supply duplicates.] Provision was made for one major change in the type of vaporization. One of the variables in this type of determimtion is the percentage of the original material vaporized ; therefore this design must provide for varying the quantity of condensate that is held up in the reservoir. Elnowing this value, the per cent vaporized is easily calculated; and .the equilibrium temperature of the phases is obtained from the thermometer in the boiler. A detailed drawing of the equilibrium vaporization still is shown on Figure 1. Past experience with vapor-liquid equilibrium st'ills has indicated that the temperature of the phases is one of the most difficult variables to determine. Rectification, caused by condensed vapor on the walls of the boiler, can easily give an error in this value of several degrees. To prevent this, Nichrome resistance wire was wrapped around all the critical areas. When supplied with electrical energy, these heat.ing units maintained the walls a t a sufficiently high temperature to keep the vapor from condensing. The ~ ~ - a lwere l s covered Kith thermal insulation; and thermocouples were embedded therein, so t'hat the electrical heaters could be controlled to keep the outside of the flask wxlls a t the same temperature as the still itself. The size of the charge required for operation of the unit i3 important. An oversize unit would be clumsy in glass, woulcl require a large quantity of test material, and thus would lose one of it's chief advantages. On the other hand, too small a charge would make heating of the liquid difficult a t the point of 90% vaporized, and errors of measurement might be more important. From these considerations a charge of 500 ml. appears movt desirable. The bottom sect.ion of the boiler was fabricated with a smaller bubble, so that the depth of the liquid was sufficient for heating when most of thc charge wa8 in the condensate reservoir. A large clean-out opening was supplied a t the top to allow for removal of any sludge formed. This opening was fitted wit,li an evacuated ball stopper in a standard socket; it may be eliminated when working with most charge stocks, which give nothing in the flask that. cannot be cleaned by solvent action. Two thermometer wells were placed in the boiler (one through the top ball stopper), so that the temperature of both the liquid and the vapor can be measured. During operation of the unit, it was found that the temperature of the liquid could be held constant, and the temperature of the vapor varied by means of the external heating coils, over a' range of approximately 20" F. Petroleum vapors wet the glass walls of the still; and any condensation formed was not noticeable. Because the vapor temperature could be independently varied, the liquid temperature was used as the equilibrium value and the boiler jacket heating element was adjusted so that t,he vapor temperature equaled the liquid temperature. This method of operation gave reliable results when the ethyl alcohol-water system was tested and compared with published data. A third thermometer well was placed in t,he vapor arm, so that the temperature of the vapors passing into the condenser could be measured. During the evaluation of heavier stocks, it is desirable t o keep this tempcrature a t a minimum, in order to prevent thermal decomposition. An internal heating element consisting of a spring-wound Nichrome wire was used, so that bumping and superheating of the liquid would be eliminated. This also allowed the smooth boiling of even small liquid volumes. The condenser Tvas constructed in two parts, so that wax1 fractions could be handled. The firEt condenser consisted of four balls and could be operated a t a temperature just sufficient' to condense the higher boiling portion of the vapors and still allow the condensate to flow freely down the walls without freezing out the wax. The lighter materials were then condensed in a second ball condenser which could be operated a t as low a temperaturc aq required This method of condensation allowed ample flexibility
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1951
in the operation of the unit, and is recommended especially for ' subatmospheric studies or whenever there is a wide range in the volatilities of the components in the charge. For convenience, the second condenser was a separate unit connected with a T 24/40 joint. The receiver or condensate reservoir was graduated from 10 to 450 ml. in 10-ml. divisions. Every 100 ml. the graduations followed completely around the wall of the receiver to reduce the possibility 'of parallax in the readings. A short, tapered inlet nozzle to the reservoir allowed the counting of drops of condensate, which served to measure the rate of boiling. The condensate receiver was enclosed in the same water jacket as the *first condenser in order to maintain the proper temperature for volumetric measuring. Jacket nozzles at top and bottom of the condenser section and a t bottom of the reservoir allowed control of the t,wo sections by varying the amounts of water flowing past each. A three-way stopcock, placed in the 3-mm. capillary tube leading from the condensed vapor reservoir to the reboiler, was used for controlling the recycle runback and thus maintaining the proper volumes in the reservoir and in turn in the boiler. This cock Kas also used for taking samples of the liquid and of the condensate as well as for draining the equilibrium still. A pointer was attached to the cock by means of a Hamilton fastener, so t h a t the proper recycle position could be readily attained, as indicated by a circular scale. The complete laboratory setup for determining equilibrium vaporization data is shown on Figure 2. Temperatures of the various thermocouples were read by means of a Leeds & Northrup Type K potentiometer with standard accessories. Water from a constant temperature bath was fed into the condenser nozzles and maintained at the desired level by means of an, adjustable overflow arm. A dry ice trap was used in the line leading from the vent condenser, so that light ends and gases formed by cracking of the charge might be detected escaping from the still. -In absolute manometer (6)was used for measuring the PresSure on the unit, maintained by 8. Cartesian-tYPe manostat (7) supplied by the Emil Greiner Co. All the indicating devices on the unit were carefully tested and calibrated a t frequent intervals throughout the investigation t o reduce the experimental error.
STILL
DRY ICE TRAP
Figure 2. C.
1609
TESTING OF EQUILIBRIUM STILL
Several factors were considered pertinent in deciding whether the unit was satisfactory for obtaining the desired data: the pressure drop between boiling liquid and pressure-measuring device; the possibility of entrainment of droplets from the boiling liquid to the condensate ;eceiver; and the approach of liquid and vapor t o equilibrium conditions. A differential manometer placed between the boiler and the regular absolute manometer did not indicate a noticeable pressure drop when the unit was operated under extremely adverse conditions-i.e., 3 mm. of mercury absolute pressure and a boil-up of 140 drops per minute as measured on the condenser drop counter. Tests made with a dye, Sudan Red, dissolved in a petroleum cut showed the entrainment t o be about 0.2 p.p.m. a t the very high rate conditions of the pressure drop determination. This is a negligible entrainment for satisfactory operation of the equilibrium still, which was usually operated at a much slower rate. In order to determine if the unit actually produced equilibrium values, the ethyl alcohol-water system which had been studied by several investigators ( 2 , 10)was examined and the still was operated in accord with previous practice and by the method given below. The results were in excellent agreement with the accepted values of Carey and Lewis (k?), from which none of the experimentally determined values deviated more than the small experimental error of either the literature or these determinations. The equilibrium data themselves were compared with those of Carey and Lewis; and an experimental flash curve was run as outlined below for a charge stock of a 29y0 ethyl alcohol-water solution. It is possible to calculate readily the shape of its flash curve from the equilibrium and boiling point data for a binary solution; the determined curve coincided with that calculated from the Carey and Lewis data. OPERATING PROCEDURE
The operating technique developed depended somewhat on the characteristics of the particular petroleum crude or fraction. The sample was placed in a beaker and cooled t o a temperature of 60" F. If wax Particles separated, the material was warmed until these disappeared. All volumetric measurements were made a t or above this temperature of complete solubility. A charge of 500 ml. was then measured a t the standard temperature for the given sample and added t o the clean equilibrium still, with the regulating valve closed. I n measuring the charge, care was taken t o get all the material in the still by filling the graduate t o a higher level and adding 500 ml. without draining the graduate completely. If the material was clear and not too viscous, it was added t o the condensate reservoir through the vent condenser groundglass joint. After coming to the proper measuring temperature, as controlled by the temperature of the water jacket, it flowed through the regulating valve into the boiler. If the material was black and viscous, it was added through the thermometer
MANOMETER
MANOSTAT
VACUUM PUMP
Equilibrium Vaporization Unit
Condenser nozzle. T. Thermocouple junction. TH. Thermometer. All heating coils connected to variable transformers
INDUSTRIAL AND ENGINEERING CHEMISTRY
1610
Vol. 43, No. 7
E w
J
w
a
W
IK U
I>
W P
z
W K
a
W
I-
W
I-
e0
loot!
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40
50
60
70
80
90
IO0
100 0
10
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30
40
50
60
70
BO
90
100
PERCENT VAPORIZED
Figure 4.
E q u i l i b r i u m F l a s h \ a p o r i z a t i o n Curves for > l i d - C o n t i n e n t Hear? N a p h t h a Stork 2
well nozzle or the large top opening. With very viscoue and waxy fractions, the charge a t a n elevated temperature was taken from a container weighed before and after. The difference divided by the density a t 60" F. gave the volume. After the still was charged, cooling Rater was supplied t o the vent condenser and the main condenser. Dry ice was placed in the trap t o condense very volatile materials. (If more than 2 ml. of condensate were collected in the trap during a run, an air leak was suspected and eliminated.) The system was evacuated to the desired operating pressure, and the heating elements were connected. The temperatures of the boiler wall and vapor arm were maintained a t a point slightly higher than the expected initial boiling point of the liquid. Gradually the liquid temperature was increased until the first drop fell from the drop counter a t the bottom of the condenser. (In repetition of work with the same stock it was found that the first drop did not always come over a t the same temperature, whereas the fifth drop did. The initial temperature point was therefore always recorded a t the fifth drop.) The rate of distillation was then adjusted t o a standard of 120 drops per minute, although, depending on the nature of the material being handled, some lower or faster rates were used occasionally. When the condensate level reached the 50-ml. graduate, the regulating valve was opened slightly, and the liquid was recirculated back into the boiler. If the condensate was particularly volatile or its return too sudden, bumping occurred. I n many cases, it was found preferable to Ehut off the boiler heater just before starting the recycle. Other methods were considered for automatically controlling the recycle and the volume of condensate in the reservoir, hence the effective per cent vaporization. One was a multiplicity of branch overflow lines with cocks a t different levels from the reservoir back to the still bottom; the lower ones, being closed, would maintain the level at that of the first open one. Another possibility was an inverted U siphon line with a multiplicity of cocks, or two ground joints for a swing connection, to control its height. A11 these devices were much more complicated; and the simple regulating valve
used was found to be entirely effective and simply operated to control the flowback a t any desired operating rate and level in, the condenser. Boiling, condensing, and recirculation were continued until the liquid' and vapor temperatures remained constant for a t least 15 minutes, a t which time temperature readings were taken indicative of equilibrium conditions under 10% vaporizationLe., the 50 ml. of condensate in the reservoir were of the same composition as the vapors being formed and amounted to 10% of the charge. The time necessary for reaching equilibrium conditions b e tw-een vapor and liquid was found t o be from 0.5 t o 4 hours, depending on the nature of the material and particularly the per cent vaporized. That the longest time should theoretically be for about 50% vaporized was borne out in practice. Some small error is involved in possible liquid holdup present, as a film in the condenser. KO definite estimate of this amount can be made, because it is different under the dynamic conditione of operation and the static conditions of a final shutdown. The amount is not large, or the check runs with alcohol and water could not have agreed with the calculated curve. However, with petroleum fractions some small error may exist which will always be consistent for the same stock and will lead t o constant relative values in using data from the still. Additional points were run off for other values of the per cent vaporized, such as 20, 30%, etc., up to 90 or 95%. -4fter the test for the highest percentage vaporization was run, the lOye point was rerun t o check that point and to make 8ure that cracking had not taken place throughout the entire test. Finally, the material drained from the still was again mcasured
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1951
800
a t the staiidiLrd temperature as a cheek on possible mistakes or losses.
F
i /
WITH RESULTS FROM CONTINUOUS UNIT
CO4Il'AHISOh
While it was always possible t o check equilibrium flash vaporization curves on different samples of the same material, it seemed desirable t o check the data obtained in this still with those obtained in a continuous unit. The Socony-Vacuum Oil Co. has such a unit, similar in design t o that of Edmister et al. ( 4 ) but larger. This unit has not been tested for entrainment, pressure drop, or equilibrium conditions. Unfortunately, as there was available only one sample of material which had been run in this unit, a comparison with various cuts of petroleum was impossible. (The continuous unit has not been standardized; it appears t h a t the units have been little used even by the few companies that have built them.) The one available sample was tested in the present unit to give:
%
Vaporized 1.b.p.
10
47.1
P E R C E N T VAPORIZED
Figure 5.
1611
Equilibrium Flash Vaporization Curves for Mid-Continent Heavy Gas Oil
Continuous Unit Socony, F.
Recirculating
..
288 376 510
500
"t,
F.
This discrepancy of 10" F. can be accounted for by condensation in the vapor-liquid separator of the Socony unit. The condensation gives a smaller indication of the per cent vaporized than actually occurred as indicated by the engineer in charge of the continuous unit. A review of Socony data on other crudesno samples of which remain-indicated t h a t their values were not reproducible to within * 10' F. The only conclusion t h a t can be drawn is qualitative rather than quantitative-Le.. t h a t the two units give results in the same range.
Stock 3
700
-
s0
/'
-
PRESSURE
I
700
30v 200b
'
IO
Figure 6.
20
30
50 60 70 PERCENT VAPORIZED.
40
80
90
Equilibrium Flash Vaporization Curves for Iraq Light Gas Oil Stock 4
300 0
10
Figure 7 .
20
30
40 50 60 70 PERCENT VAPORIZE0
80
90
0
Equilibrium Flash Vaporization Curves for Utah neasphalted Oil Stock 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
1612
bccn thoroughly t'ested; and unstandardized techniques may account for the difference in temperature shown. I n general, as the continuous unit has not been standardized as a test.irig unit, for analytical or design results, and even the same unit is known to give results which are not reproducible, the developed unit and technique may better be considered on their own nicrits without such comparison.
TABLE I. INSPECTIONS O F TESTSAMPLES MidEast ConTexas tinent Heavy Heavy Naphtha Naphtha 1 2 50.4 51.8
MidContinent Heavy Gas Oil 3 28.0
Description Stock l i o . O API ASThIo I.b.p., F. 224 254 '% 263 lo% 273 20% 30% 294 282
Utah Deasphalted Oil 5 24.8
Iraq Light Gas Oil 4 27.3
Coastal Crude 6 24.2
Ilaifa Reduced Crude 7 16.8
250 $82" 346a 541" 292a 020 495 584 418 281 561 552 615 466 288 29.5 624 623 668 522 303 662 673 715 556 709 709 761 597 310 50 92 316 754 540 814 637 303 60 70 312 323 802 764 866 652 322 330 852 788 927 663 80 70 912 812 1017 684 7070 334 340 90% 353 356 1000 847 ... 95% 373 380 ... 883 ... ... ... ... ... ... E.P. 399 422 0 Corrected from vaciium. D a t a were obtained from various companies. Original vacuum d a t a for stocks 3 able.
"'
1 . .
Another sample, which had been run in the continuous unit of the Standard Oil Dpvelopment Co. (Kew Jersey), was tested.
Pressure, 111111. Temperature, F. To vaporized Viscosity, S.S.U. at 220" F. (overhead) Gravity (overhead), A.P.I.
Continuous Unit SODCO 4.5 429 22 34.5 31.1
Recirculating Unit 4.5 444 22 35.1 31.4
At first it was believed that the difference in tempprature might be due to superheating of the liquid a t this low pressure. A thermocouple search, made inside t h r boiler of the present unit, indicated that the thermometers were reading correctly and that there was a 1" temperaturp increase between the surface of the boiling liquid and a point approximately 8.5 cin. helow the surface The closeness of this point to the internal heater is probably the reason for thr increase. I t appears from these results that the amount of superheat is negligible The continuous unit had not
0
10
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70
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90
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567 651 740 so5 868 922
... ... ...
...
Wax Fiirnace Charge 8 41.0 687a 703 708 713 721 730 739 733 77 1 797 831 852
Equilibrium Flash Vaporization Curves for Coastal Crude Stock 6
PRESENTATIOTI- OF DATA
The inspections of the various pptroleuin samples used in this work arc present'ed in Table I. The A S T h t o 8 were not availprocedure is not applicable t,o inany of t,he higher boiling fractions and i t was necessary to perform these differential distillations under a vacuum of 10 mm. of mercury absolute pressure. The values obtained were transformed t o atmospheric pressurr, so that all values are on an equivalent basis. In Figures 3 t o 10 are pieseiited equilibrium flash vaporization curves for eight petroleum fractions. These data have been corrected for known errore in thermometei stem emergence, atmospheric pressure deviations from 760 mni., and volume of liquid corresponding to that represented by the noncondensed vapor. The first two items were corrected by standard methods. The ...
...
...
ou"c
-"-0
IO
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80
SO
100
P E R C E N T VAPORIZED
VOLUME PERCENT VAPORIZED
Figure 8.
Vol. 43, No. 7
Figure 9.
Equilibrium Flash Vaporization Curves for Haifa Reduced Crude Stock 7
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1951
/-
2 0 0 M M . PRESSURE
ay
b7;%:=?'1
+ 500
400
0
10
Figure 10.
20
30
40 50 60 70 PERCENT VAPORIZED
80
90
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Equilibrium Flash Vaporization Curves for Wax Furnace Charge
1613
Consistent and reproducible readings with mixtures of a large tern erature spread may be obtained. T i e still has only one valve and therefore a minimum of chance for leakage. When light naphthas are run in the continuous units, valves often require repacking owing t o the high solvent action. This is not true with the unit presented here. Three-quarters of an hour to 4 hours are DISADVANTAGES. required t o reach equilibrium between vapor or liquid. (This time is not considerable, however, compared t o the time required t o come t o a desired steady state with the continuous unit.) As a consequence, thermally unstable stocks must be run a t temperatures no higher than 650 F. t o prevent decomposition. Adequate and simple methods are available, however, for conversion of data so obtained under vacuum conditions to atmospheric conditions. Points higher than about 92% vaporized must be obtained in auxiliary equipment. These data, however, are usually not needed. I n equilibrium tests on eight different samples, a t total pressures on the system varying from atmospheric to 3 mm., the unit gave excellent performance and consistent, reproducible results. The mixtures included naphthas, gas oils, crude oils, reduced crude, and a waxy furnace charge.
Stock 8
ACKNOWLEDGMENT
third quantity is usually negligible, but the method of correction would be used in very precise work. As a n example, i t is desired t o find the quantity of uncondensed vapor in the equilibrium unit for the mid-continent heavy naphtha, 10% vaporized point at atmospheric pressure. From the inspection of the initial petroleum fraction and basic still measurements, the following information may be extracted: ASTM 50% point, 316" F. Gravity, 51.8"A.P.I., or 0.7720 gram per ml. Total volume of boiler and transfer arm, 1308 ml. Vapor line temperature, 295' F. Molecular weight by Watson correlation (18), 135 Using the simple gas law, = NRT,where R = 45.6 45.6 (295 460) 1 (1308 - 4 5 0 ) = 135 where g = 3.37 grams Assuming t h a t the density of the condensate is close t o t h a t of the charge, the correction for the noncondensed vapor is 3 37 or 4.37 ml. This correction is added t o the observed
PV
+
Many of the petroleum samples and some of the equipment used in this investigation were supplied by the M. W. Kellogg Co. The Standard Oil Co. of New Jersey and the SoconyVacuum Oil Co. also aided in this work. Roger Gilmont of the Emil Greiner Co., 22 North Moore St., New York, N. Y . , nas extremely helpful in offering suggestions and in supplying the equilibrium still. Finally, cordial appreciation is expressed to L. C. Knox, development engineer of the Sun Oil Co., Marcus Hook, Pa., whose earlier work suggested this study and whose kind comments were invaluable during its progress. NOMENCLATURE
N P
R
= number of gram moles = total pressure
= gas law constant 4' = absolute temperature V = molar volume
0.7720,
condensate volume of 48 ml., giving a total of 52.4 ml. Dividing by the total volume of the charge, 500 ml., the fraction of the volume va orized at the equilibrium temperature equals 10.5%. At reduce$ pressures, this correction greatly decreases in magnitude. CONCLUSIONS
This equilibrium unit allows the simple determination of data previously obtained only with difficulty and expense The unit has been found satisfactory for operating pressures between 3 and 760 mm., and temperatures from 100' t o 675 F., depending upon the thermal stability of the test sample. The still has been shown t o be satisfactory as regards entrainment, pressure drop, and approach t o equilibrium conditions. This unit has several advantages and disadvantages when compared with the continuous type of unit currently in use. ADVANTAGES.It is a compact unit which may be set up in a laboratory bench top. The initial cost is a fraction of that for the continuous type. Only a small quantity of charge material is required per determination-e.@;., 500 t o 2000 ml. per flash curve as compared with approximately 2 barrels for the continuous type. It requires a minimum of routine attention from one operator, who may carry on other work concurrently. This unit allows the determination of the initial boiling point of the mixture and all points of vaporization up t o about 92%. There is negligible pressure drop through the unit. This allows reading of the pressure a t a point where condensing vapors do not clog the manometer.
LITERATURE CITED
Bahlke, W. H., and Kay, W. B., IND.ENG.CHEM., 15, 5923 (1923).
Carey, J. S.,and Lewis, W. K., Ibid., 24,883 (1932). Edmister, W. C., and Pollock, D. H., Chem. Eng. Progress, 44, 905-26 (1948).
Edmister, W.C.,Reidel, J. C., and Mervin, W. J., Trans. Am. Inst. Chem. Engrs., 39, 437 (1943). Fancher, G., PetroEeum Engr., 2, 176-80 (1931). Gilmont, R., Anal. Chem., 20, 474 (1948). Gilmont, R., IND.ENG.CHEM.,ANAL.ED.,18, 633 (1946). Helmers, C. J., Johnson, P. H., and Mills, K. L., Oil Gus J.,47,
NO. 7 , 85-90 (1948). Leslie, E. H., and Good, A. J., IND. ENG.CHEM.,19, 453 (1927). Noyes, W. A., and Warfle, R. R., J . Am. Chem. SOC.,23, 468 (1901).
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